The dermis makes up the bulk of the skin and is mainly composed of fibroblasts and matrix components. Fibroblasts produce proteins such as collagen as well as glycosaminoglycans such as hyaluronic acid to form connective tissue, and are thus play an important role in the skin. The reduction of the fibroblast functions due to aging or other causes may lead to the reduction and degeneration of collagen, hyaluronic acid and other matrix components. Oxidative stress such as ultraviolet light also damages the skin and makes it rough, and causes other adverse effects. Due to the reduction of the matrix components and oxidative stress, aging of the skin occurs, which causes wrinkles, spots, dull appearance, the loss of the smooth texture, the reduction of the elasticity, and other signs of aging.
The functions of collagen and hyaluronic acid have drawn attention as a target for preventing aging of the skin. Conventionally, hyaluronic acid derived from cockscombs or other origins is added to anti-aging agents. However, hyaluronic acid is a high molecular weight molecule, and thus even when hyaluronic acid cosmetics are directly applied to the skin, hyaluronic acid is difficult to be absorbed to the skin. Collagen injections to the skin are also used, but the injected collagen disappears from the skin in a short period of time. Subcutaneous implant therapy using fibroblasts derived from autologous stem cells is also attempted, but the implanted fibroblasts are difficult to remain at the site of implantation.
To address these problems, a search has been actively conducted for natural substances that promote the growth of fibroblasts in the dermis and thereby enhance the production of collagen and hyaluronic acid by the cells. Many natural substances with such an effect have been reported, including various plant-derived substances such as an aqueous chlorella extract, an aloe vera extract, a prickly pear extract, an apricot kernel extract and a passion flower extract.
A peptide of 20 amino acid residues or less is easy to design, and efficient synthetic methods and analysis methods therefor have already been established. Such a peptide thus has the advantage of mass production at low cost. Another advantage is that the peptide is less antigenic and hence when used as an ingredient of a pharmaceutical product, the peptide is less likely to cause adverse side effects. The peptide is very close to practical applications as an ingredient of quasi-drugs or cosmetics. A further advantage is that the peptide contains naturally occurring amino acids and hence is safe with no irritating or sensitizing properties and easily metabolized. There is therefore no obstacle to advancing research and development.
Peptides with various physiological activities, such as the effect of promoting fibroblast growth, are expected to be discovered and developed.
An attempt has been made to improve the skin conditions by applying peptides to the skin. Patent Literature 1, for example, discloses an anti-aging preparation for cutaneous application and an anti-aging cosmetic preparation, the preparations each comprising component (A) a synthetic peptide of 3 to 8 amino acids or a derivative thereof, and component (B) a hydrolyzed collagen with a molecular weight ranging from 500 to 5,000 or a derivative thereof. However, Patent Literature 1 does not disclose an anti-aging preparation for cutaneous application or anti-aging cosmetic preparation comprising a peptide as a single active ingredient.